Liquid crystal display panel and fabricating method thereof

ABSTRACT

A liquid crystal display panel including a first substrate, a second substrate, a liquid crystal layer, and a polymer stabilized alignment layer is provided. The second substrate is disposed opposite to the first substrate. The liquid crystal layer is disposed between the first substrate and the second substrate. The polymer stabilized alignment layer is disposed between the first substrate and the liquid crystal layer, and an average surface roughness of the polymer stabilized alignment layer is greater than or equal to 10 nm.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 97127656, filed on Jul. 21, 2008. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display panel and a fabricatingmethod thereof, and more particularly to a liquid crystal display (LCD)panel and a fabricating method thereof.

2. Description of Related Art

Conventionally, the multi-domain vertically aligned liquid crystaldisplay (MVA-LCD) panel utilizes an alignment structure to make liquidcrystal molecules in different regions tilt at different angles toachieve the effect of wide viewing angle. The alignment structureincludes alignment protrusions and alignment slits disposed onelectrodes. However, light leakage usually occurs due to thedisclination in tilt directions of the liquid crystal moleculessurrounding the alignment protrusions and the alignment slits, whichalso leads to reduction of the contrast ratio of the LCD panel. Toreduce light leakage, light-shielding layers disposed corresponding tothe alignment protrusions and the alignment slits would cause theaperture ratio of the LCD panel to decrease.

Therefore, the prior art has proposed a polymer stabilized alignment(PSA) process to improve the poor display contrast in the MVA-LCD panel.In the polymer stabilized alignment process, first, reactive monomersare mixed in the liquid crystal layer and a specific voltage is appliedto the liquid crystal layer. Under such specific voltage, the liquidcrystal layer are irradiated with light or heated to polymerize thereactive monomers so that polymer stabilized alignment layers are formedat the junctions of the liquid crystal layer and substrates. The polymerstabilized alignment layers with specific alignment effects assistliquid crystal molecules of the liquid crystal layer to tilt and alignin different directions to achieve the effect of wide viewing angle. Inaddition, the polymer stabilized alignment layers can function assubstitutes for the alignment protrusions and the alignment slits, sothe light leakage of the LCD panel does not occur and the displaycontrast in the LCD panel is enhanced. Moreover, the polymer stabilizedalignment layer stabilizes the liquid crystal molecules at the junctionsof the liquid crystal layer so that the liquid crystal layer has asatisfactory response time.

SUMMARY OF THE INVENTION

The present invention provides a liquid crystal display (LCD) panelhaving a polymer stabilized alignment layer with an average surfaceroughness greater than or equal to 10 nm.

The present invention further provides a fabricating method of an LCDpanel to form a polymer stabilized alignment layer having an averagesurface roughness greater than or equal to 10 nm between a liquidcrystal layer and a substrate.

The present invention provides an LCD panel including a first substrate,a second substrate, a liquid crystal layer and a polymer stabilizedalignment layer. The second substrate is disposed opposite to the firstsubstrate. The liquid crystal layer is disposed between the firstsubstrate and the second substrate. The polymer stabilized alignmentlayer is disposed between the first substrate and the liquid crystallayer, and the average surface roughness Rms of the polymer stabilizedalignment layer is greater than or equal to 10 nm.

According to an embodiment of the present invention, 10 nm≦Rms≦40 nm.

According to an embodiment of the present invention, 10 nm≦Rms≦30 nm.

According to an embodiment of the present invention, a material of thepolymer stabilized alignment layer is an optically polymerized materialor a thermally polymerized material.

According to an embodiment of the present invention, the polymerstabilized alignment layer is formed by polymerizing a monomer material.The monomer material is expressed in a chemical formula [1]:B-A-R  [1]

wherein A is selected from chemical formulae [2], [3], [4] or anycombination of the foregoing,

and at least one of B and R is selected from alkyl group, alkoxyl group,ester group, chemical formulae [5], [6], [7] or any combination of theforegoing:

Wherein T is selected from oxygen, nitrogen or any combination of theforegoing; X is selected from hydrogen, alkyl group, halogen, cyanogroup or any combination of the foregoing; n is a positive integer.

According to an embodiment of the present invention, the liquid crystallayer has a plurality of vertically-aligned liquid crystal molecules,and the liquid crystal molecules are aligned at a pre-tilt angle.

According to an embodiment of the present invention, the first substrateand the second substrate are interchangeably a switch device arraysubstrate and an opposite substrate.

According to an embodiment of the present invention, the LCD panelfurther includes a first alignment layer disposed between the polymerstabilized alignment layer and the first substrate.

According to an embodiment of the present invention, the LCD panelfurther includes a second polymer stabilized alignment layer disposedbetween the second substrate and the liquid crystal layer.

According to an embodiment of the present invention, the LCD panelfurther includes a second alignment layer disposed between the secondpolymer stabilized alignment layer and the second substrate.

The present invention further provides a fabricating method of an LCDpanel. The fabricating method includes the following steps. First, afirst substrate and a second substrate are provided. Next, a liquidcrystal mixed material is sealed between the first substrate and thesecond substrate. The liquid crystal mixed material includes a liquidcrystal composition, a monomer material and a polymerization initiator.Afterwards, a plurality of liquid crystal molecules in the liquidcrystal composition is aligned at the pre-tilt angle. Thereafter, themonomer material is polymerized to form the polymer stabilized alignmentlayers between the liquid crystal mixed material and the first substrateand between the liquid crystal mixed material and the second substrate,respectively. An average surface roughness Rms of the polymer stabilizedalignment layer is controlled as greater than or equal to 10 nm.

According to an embodiment of the present embodiment, 10 nm≦Rms≦40 nm.

According to an embodiment of the present embodiment, 10 nm≦Rms≦30 nm.

According to an embodiment of the present invention, the step of sealingthe liquid crystal mixed material includes performing a one drop fill(ODF) process.

According to an embodiment of the present invention, the step ofaligning the liquid crystal molecules in the liquid crystal compositionat the pre-tilt angle includes applying an electrical field on theliquid crystal molecules.

According to an embodiment of the present invention, the step ofpolymerizing the monomer material includes performing an irradiatingprocess or a heating process on the monomer material and thepolymerization initiator.

According to an embodiment of the present invention, the irradiationprocess employs an ultraviolet light source.

According to an embodiment of the present invention, the irradiationprocess includes performing a first irradiation step and a secondirradiation step on the monomer material and the polymerizationinitiator.

According to an embodiment of the present invention, an irradiationintensity of the first irradiation step is between about 0.2 mW/cm² andabout 200 mW/cm², and an irradiation time is between about 10 secondsand about 10 hours, preferably between about 120 seconds and about 1800seconds.

According to an embodiment of the present invention, the irradiationintensity of the second irradiation step is between about 0.2 mW/cm² andabout 200 mW/cm², and the irradiation time is between about 10 secondsand about 10 hours, preferably between about 1 hour and about 6 hours.

According to an embodiment of the present invention, the first alignmentlayer is formed on the first substrate before the liquid crystal mixedmaterial is sealed.

According to an embodiment of the present invention, the secondalignment layer is formed on the second substrate before the liquidcrystal mixed material is sealed.

In the LCD panel of the present invention, the average surface roughnessRms of the polymer stabilized alignment layer disposed between thesubstrate and the liquid crystal layer is controlled as 10 nm≦Rms≦40 nmto enhance an aligning ability of the polymer stabilized alignment layeron the liquid crystal molecules, improve a response time of the LCDpanel and reduce image sticking. Therefore, the LCD panel achievessatisfactory display characteristics, such as fast response time, lowlight leakage, high contrast and low image sticking.

In order to make the above and other objects, features and advantages ofthe present invention more comprehensible, several embodimentsaccompanied with figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 shows the relationship between the average surface roughness Rmsof polymer stabilized alignment layer and its related response times(Tr, Tf and T) in Table 1.

FIG. 2 is a schematic cross-sectional view of an LCD panel according tothe first embodiment of the present invention.

FIG. 3 is a flowchart of fabricating an LCD panel according to thesecond embodiment of the present invention.

FIGS. 4A through 4D show schematic cross-sectional drawings offabricating an LCD panel according to the second embodiment of thepresent invention.

FIG. 5 is a schematic cross-sectional view of an LCD panel according tothe third embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Table 1 is the result of testing LCD panels having polymer stabilizedalignment layers with different average surface roughness Rms. FIG. 1shows the relationship between an average surface roughness Rms of thepolymer stabilized alignment layer and its response times (Tr, Tf and T)in Table 1. Table 1 shows a tendency between the average surfaceroughness Rms of the polymer stabilized alignment layer in the LCD paneland the related response time. Tr represents the response time requiredfor a transmittance ratio of the LCD panel increasing from 10% to 90%;Tf represents the response time required for the transmittance ratio ofthe LCD panel decreasing from 90% to 10%, and T=Tr+Tf. In other words,the smaller T is, the faster response time of an LCD panel surface wouldbe.

TABLE 1 Experimental Response Time (ms) Example Tr Tf T Rms (nm) 1105.88 6.08 111.96 2.871 2 97.51 12.94 110.45 7.23 3 95.453 6.123 101.579.015 4 20.12 5.78 25.9 11.23 5 12.38 6.84 19.22 15.86 6 6.27 9.02 15.2923.691 7 6.27 9.41 15.68 25.321 8 5.71 10.14 15.84 39.48

Referring to both Table 1 and FIG. 1, when the average surface roughnessRms of the polymer stabilized alignment layer is greater than or equalto 10 nm, the response time of the LCD panel becomes faster. In otherwords, within this range, the polymer stabilized alignment layer has abetter ability to align and stabilize liquid crystal molecules, andthereby speed up the response time of the LCD panel to prevent imagesticking in the LCD. On the contrary, when the average surface roughnessRms of the polymer stabilized alignment layer is smaller than 10 nm, thepolymer stabilized alignment layer has a poorer aligning ability, andthe response time of the LCD panel becomes rather long. Additionally,when the average surface roughness Rms of the polymer stabilizedalignment layer is too rough, such larger than 40 nm, the contrast ofthe LCD panel would drop and an optical uniformity would deteriorate,which reduces the reliability of the LCD panel. Therefore, in thepresent invention, the average surface roughness Rms of the polymerstabilized alignment layer is controlled as 10 nm≦Rms≦40 nm so that theLCD panel achieves satisfactory display characteristics, such as fastresponse time, low light leakage, high contrast and low image sticking.In particular, when the average surface roughness Rms of the polymerstabilized alignment layer is controlled as 10 nm≦Rms≦30 nm, the LCDpanel has an even better contrast and a faster response time and therebyeffectively prevents image sticking.

First Embodiment

FIG. 2 is a schematic cross-sectional view of an LCD panel according tothe first embodiment of the present invention. Referring to FIG. 2, anLCD panel 100 includes a first substrate 102, a second substrate 104, aliquid crystal layer 106 and a polymer stabilized alignment layer 108.The first substrate 102 is, for example, an active or passive switchdevice array substrate. The second substrate 104 is an oppositesubstrate disposed opposite to the first substrate 102, such as a colorfilter substrate. The liquid crystal layer 106 is disposed between thefirst substrate 102 and the second substrate 104. The liquid crystallayer 106 has a plurality of vertically-aligned liquid crystal molecules106 a. Due to the function of a polymer stabilized alignment layer 108,the liquid crystal molecules 106 a are aligned at a pre-tilt angle θ.

According to the present embodiment of the present invention, thepolymer stabilized alignment layer 108 is disposed between the firstsubstrate 102 and the liquid crystal layer 106. An average surfaceroughness Rms of the polymer stabilized alignment layer 108 is 10nm≦Rms≦40 nm. A material of the polymer stabilized alignment layer 108is an optically polymerized material or a thermally polymerizedmaterial. The polymer stabilized alignment layer is formed bypolymerizing a monomer material, for example. The monomer material isexpressed in a chemical formula [1]:B-A-R  [1]

Wherein A is selected from chemical formulae [2], [3], [4] or anycombination of the foregoing:

Wherein at least one of B and R is selected from alkyl group, alkoxylgroup, ester group, formulae [5], [6], [7] or any combination of theforegoing:

Wherein T is selected from oxygen, nitrogen or any combination of theforegoing; X is selected from hydrogen, alkyl group, halogen, cyanogroup or any combination of the foregoing; n is a positive integer.

The polymer stabilized alignment layer 108 provides alignment effect tothe liquid crystal molecules 106 a. Therefore, the liquid crystalmolecules 106 a are aligned at the pre-tilt angle θ. According to thepresent embodiment, the LCD panel 100 is, for example, an MVA-LCD panel.Hence, compared with the prior art in which only alignment protrusionsand alignment slits are disposed in the LCD panel, the polymerstabilized alignment layer 108 avoids light leakage caused bydisclination in tilt directions of the liquid crystal moleculessurrounding the alignment protrusions and the alignment slits andthereby has a better display contrast.

According to the present embodiment, the average surface roughness Rmsof the polymer stabilized alignment layer 108 is controlled as 10nm≦Rms≦40 nm. Therefore, the LCD panel 100 achieves satisfactory displaycharacteristics, such as fast response time, low light leakage, highcontrast and low image sticking. Certainly, in order to improve thecontrast and the response time of the LCD panel and effectively avoidimage sticking, in another embodiment the average surface roughness Rmsof the polymer stabilized alignment layer may be controlled as 10nm≦Rms≦30 nm. Furthermore, the foregoing embodiment is exemplified bythe polymer stabilized alignment layer 108 disposed between the firstsubstrate 102 and the liquid crystal layer 106. However, the presentinvention is not limited thereto. In other embodiments, the polymerstabilized alignment layer may be disposed between the second substrateand the liquid crystal layer. In order to further control the alignmentof the liquid crystal molecules, the polymer stabilized alignment layermay also be simultaneously disposed between the first substrate and theliquid crystal layer and between the second substrate and the liquidcrystal layer such that the LCD panel achieves some satisfactory displaycharacteristics such as fast response time, low light leakage, highcontrast and low image sticking.

Second Embodiment

FIG. 3 is a flowchart of fabricating an LCD panel according to thesecond embodiment of the present invention. FIGS. 4A through 4D showschematic cross-sectional views of fabricating an LCD panel according tothe second embodiment of the present invention.

Referring to both FIGS. 3 and 4A, first, a step S200 is performed toprovide a first substrate 302 and a second substrate 304. The firstsubstrate 302 is an active device array substrate, and the secondsubstrate 304 is a color filter substrate, for example. The firstsubstrate 302 includes a substrate (not shown) and an active layer (notshown). The second substrate 304 includes a substrate (not shown) and acolor filter (not shown). In other embodiments, the first substrate mayalso be a color filter on array (COA) substrate which integrates thecolor filter on the active layer or an array on color filter (AOC)substrate which integrates the active layer on the color filter.Correspondingly, the second substrate may be a glass substrate, aplastic substrate or other suitable substrates. In other words, thesecond substrate does not include a color filter.

Still referring to FIGS. 3 and 4A, a step S202 is performed to seal aliquid crystal mixed material 306 between the first substrate 302 andthe second substrate 304. The liquid crystal mixed material 306 includesa liquid crystal composition 308, a monomer material 310 and apolymerization initiator (not shown). The liquid crystal composition 308includes a plurality of liquid crystal molecules 308 a. Details aboutthe monomer material 310 can be referred to the monomer material in thefirst embodiment and are not reiterated herein. The polymerizationinitiator is selected from, for example, IRGACURE 184, IRGACURE 2959,IRGACURE 1000, IRGACURE 1173, IRGACURE 500, IRGACURE 651, IRGACURE 369,IRGACURE 907, IRGACURE 1300, IRGACURE 784, IRGACURE 819 and IRGACURE 819DW, IRGACURE 250, IRGACURE 2005 and IRGACURE 2010, and IRGACURE 2020,DAROCUR 1173, DAROCUR BP, DAROCUR MBF, DAROCUR 4265 and DAROCUR TPO orany combination of the foregoing. DAROCUR and IRGACURE are both productnames sold by Ciba Specialty Chemicals Co., Ltd. According to thepresent embodiment, the liquid crystal mixed material 306 is providedbetween the first substrate 302 and the second substrate 304 by a onedrop fill (ODF) process, for example.

Referring to both FIGS. 3 and 4B, afterwards, a step S204 is performedto apply an electrical field on the liquid crystal composition 308 toalign the liquid crystal molecules 308 a at a pre-tilt angle θ, forexample.

Referring to both FIGS. 3 and 4C, a step S206 is performed thereafter.At the same time when the electrical field is applied on the liquidcrystal molecules 308 a, an irradiation process is performed on themonomer material 310 and the polymerization initiator, for example, topolymerize the monomer material 310 such that a polymer stabilizedalignment layer 312 between the liquid crystal mixed material 306 andthe first substrate 302 or a polymer stabilized alignment layer 314between the liquid crystal mixed material 306 and the second substrate304 is selectively formed. An average surface roughness Rms of thepolymer stabilized alignment layers 312 and 314 is controlled as 10nm≦Rms≦40 nm. According to the present embodiment, the light irradiationprocess includes a first irradiation step and a second irradiation step.Specifically, an ultraviolet light with an irradiation intensity betweenabout 0.2 mW/cm² and about 200 mW/cm² first irradiates the monomermaterial 310 and the polymerization initiator for a period between about10 seconds and about 10 hours, preferably between about 120 seconds andabout 1800 seconds. Next, an ultraviolet light with an irradiationintensity between about 0.2 mW/cm² and about 200 mW/cm² irradiates themonomer material 310 and the polymerization initiator for a periodbetween about 10 seconds and about 10 hours, preferably between about 1hour and about 6 hours. The present embodiment is exemplified by theultraviolet light as a light source which polymerizes the monomermaterial, but the present invention is not limited thereto. In otherembodiments, some visible lights with suitable wavelengths may also beused as the light source. In addition, a heating process may also beapplied to polymerize the monomer material. In other words, anirradiation process or a heating process may be selected to polymerizethe monomer material according to the characteristics of the monomermaterial. Further, the monomer material 310 may also be used to form thepolymer stabilized alignment layers 312 and 314 between the liquidcrystal mixed material 306 and the first substrate 302 and between theliquid crystal mixed material 306 and the second substrate 304simultaneously.

Referring to FIGS. 3 and 4D, after forming the polymer stabilizedalignment layers 312 and 314, the electrical field is removed. Due tothe aligning function of the polymer stabilized alignment layers 312 and314, the liquid crystal molecules 308 a remain aligned at the pre-tiltangle θ such that the LCD panel 300 has the characteristic of wideviewing angle.

According to the present embodiment, since the polymer stabilizedalignment layers 312 and 314 are disposed on the first substrate 302 andthe second substrate 304, and the average surface roughness Rms of thepolymer stabilized alignment layers 312 and 314 are controlled as 10nm≦Rms≦40 nm, the LCD panel 300 has satisfactory display characteristicssuch as fast response time, low light leakage, high contrast and lowimage sticking. Certainly, in order to further improve the contrast andthe response time of the LCD panel and effectively avoid image sticking,the irradiation intensity and the irradiation time in the irradiationprocess may be controlled to render the average surface roughness Rms ofthe polymer stabilized alignment layer as 10 nm≦Rms≦30 nm.

Third Embodiment

FIG. 5 is a schematic cross-sectional view of an LCD panel according tothe third embodiment of the present invention. An LCD panel 300 a has astructure similar to a structure of the LCD panel 300 in FIG. 4D, andthus the same components will be indicated with the same referencenumerals. According to the present embodiment, in order to improve thealigning ability on the liquid crystal molecules, an alignment layer 316and an alignment layer 318 are formed between the polymer stabilizedalignment layer 312 and the first substrate 302 and between the polymerstabilized alignment layer 314 and the second substrate 304respectively. In other words, in the flowchart of fabricating the LCDpanel in the second embodiment, before sealing the liquid crystal mixedmaterial 306, the alignment layers 316 and 318 are formed on the firstsubstrate 302 and the second substrate 304 respectively. A material ofthe alignment layers 316 and 318 is, for example, polyimide or othersuitable materials.

According to the present embodiment, the polymer stabilized alignmentlayers 312 and 314 are disposed on the first substrate 302 and thesecond substrate 304, and the average surface roughness Rms of thepolymer stabilized alignment layers 312 and 314 are controlled as 10nm≦Rms≦40 nm for satisfactory display characteristics such as fastresponse time, low light leakage, high contrast and low image sticking.Moreover, the alignment layers 316 and 318 are further disposed on theLCD panel 300 a to further improve the aligning ability on the liquidcrystal molecules.

The foregoing embodiment is exemplified by disposing the alignmentlayers simultaneously on the first substrate and the second substrate.However, the present invention is not limited to the example. In otherembodiments, the alignment layers may also be solely disposed on thefirst substrate or the second substrate. In other words, when thesubstrate has an alignment layer, the polymer stabilized alignment layeris disposed between the alignment layer and the liquid crystal layer.When the substrate does not have an alignment layer, the polymerstabilized alignment layer is disposed between the substrate and theliquid crystal layer.

Accordingly, in the LCD panel of the present invention, the averagesurface roughness Rms of the polymer stabilized alignment layer disposedbetween the substrate and the liquid crystal layer is controlled as 10nm≦Rms≦40 nm to enhance the aligning ability of the polymer stabilizedalignment layer so as to reduce the response time of the LCD panel andprevent image sticking. Furthermore, compared with the conventional LCDpanel with only alignment protrusions and alignment slits disposedtherein, since the polymer stabilized alignment layer avoids lightleakage caused by disclination in tilt directions of the liquid crystalmolecules surrounding the alignment protrusions and the alignment slits,the LCD panel of the present invention has a better display contrast.Additionally, the present invention defines a specific range for theaverage surface roughness of the polymer stabilized alignment layer,which improves the LCD panel through speeding up response time, andthereby provides a policy to promote the display quality of LCD panels.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the spirit and scope of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A liquid crystal display (LCD) panel, comprising: a first substrate;a second substrate disposed opposite to the first substrate; a liquidcrystal layer disposed between the first substrate and the secondsubstrate; and a polymer stabilized alignment layer disposed between thefirst substrate and the liquid crystal layer, wherein an average surfaceroughness Rms of the polymer stabilized alignment layer is in a range of15.86 nm≦Rms≦40 nm, wherein a response time required for a transmittanceratio of the LCD panel increasing from 10% to 90% is smaller than 21 msand greater than 5 ms.
 2. The LCD panel as claimed in claim 1, wherein11.23 nm≦Rms≦30 nm.
 3. The LCD panel as claimed in claim 1, wherein amaterial of the polymer stabilized alignment layer is an opticallypolymerized material or a thermally polymerized material.
 4. The LCDpanel as claimed in claim 1, wherein the polymer stabilized alignmentlayer is formed by polymerizing an monomer material expressed in achemical formula [1] as:B-A-R  [1] wherein A is selected from formulae [2], [3], [4] or anycombination thereof:

wherein at least one of B and R is selected from alkyl group, alkoxylgroup, ester group, chemical formulae [5], [6], [7] or any combinationthereof:

wherein T is selected from oxygen, nitrogen or any combination thereof,and X is selected from hydrogen, alkyl group, halogen, cyano group, orany combination thereof, n is a positive integer.
 5. The LCD panel asclaimed in claim 1, wherein the liquid crystal layer has a plurality ofvertically-aligned liquid crystal molecules, and the liquid crystalmolecules are aligned at a pre-tilt angle.
 6. The LCD panel as claimedin claim 1, wherein the first substrate and the second substrate are aswitch device array substrate and an opposite substrate interchangeably.7. The LCD panel as claimed in claim 1, further comprising a firstalignment layer disposed between the polymer stabilized alignment layerand the first substrate.
 8. The LCD panel as claimed in claim 1, furthercomprising a second polymer stabilized alignment layer disposed betweenthe second substrate and the liquid crystal layer.
 9. The LCD panel asclaimed in claim 8, further comprising a second alignment layer disposedbetween the second polymer stabilized alignment layer and the secondsubstrate.
 10. The LCD panel as claimed in claim 1, wherein the responsetime is smaller than 7 ms and greater than 5 ms.